Application of powder coatings in construction machinery

Application of powder coatings in construction machinery
Wang Kunfa
1
, Gu Guangxin
1
, Wang Shuai
2
, Ko Xiangyang
2
, Zhao Hong
2
, Xiao Jian
2
, Fang Qi
3
(1. Fudan University, Shanghai 200433; 2. Xugong Group, Xuzhou 221004; 3. Jotun Coatings Co., Ltd., Shanghai 200010)
0 Introduction
With people's growing awareness of environmental protection, national laws and regulations on environmental protection requirements are becoming more stringent, some pollution coating process is gradually restricted. Under these conditions, in order to minimize environmental pollution, the coating and coating process used in the construction machinery industry has put forward higher requirements. Since powder coatings are more economical and environmentally friendly than traditional solvent-based coatings,
of
. In recent years, with the continuous development of new products and technologies of powder coatings, it has been developed in the field of construction machinery. According to statistics, from
2003-2011
, the compound growth rate of domestic powder coating production reached
20%
, in the next few years, the average annual growth rate of powder coatings reached at least
15%

.
this paper, taking a factory powder coating line as an example, analyzes in detail the application of powder coating technology in the field of construction machinery. According to the characteristics of construction machinery parts, the construction machinery coating can be divided into: sheet coating, structural parts coating and small parts coating. This paper will discuss the application of powder coating technology in the three components of engineering machinery, summarize and analyze the characteristics and problems of powder coating technology in different components.
1Powder coating technology
1.1 powder coating application status
powder coating with low pollution,
coating efficiency, good coating performance, high economic benefits, so that its share in the construction machinery coating increased year by year. In recent years, many large-scale construction machinery manufacturers have invested heavily in the establishment of powder coating lines, so that the cost of coating operation is reduced, and small construction machinery manufacturers because of the powder coating line one-time investment, rarely set up powder coating lines. At present, the application of powder coating technology in engineering machinery mainly concentrates on sheet coating and small parts coating, such as cab, hood, ladder, bench, etc. , while the use of powder coating technology on structural parts coating examples are still few, although there are also structural parts powder coating line, but there are still more problems in its operation, mainly due to structural complexity leading to uneven baking, energy consumption, comprehensive operating costs are more expensive. In order to improve the efficiency and quality of powder coating, and taking into account the complexity of the construction machinery component structure, the construction machinery powder coating line mainly uses a combination of rediclent automatic powder and manual powder coating. In addition, there are some shortcomings in the application of powders. For example, color change difficulties, baking temperature is high, local find to make up difficulties, the construction environment requirements are high, the appearance of lacquer film orange peel is more serious.
1.2Principle of electrostitive powder coating
Powder coating has a variety of coating methods, of which electrostectrical powder coating process is currently the fastest growing in powder coating of an important construction process, but also the most common powder coating process of engineering machinery. Principle of electrostational powder spraying: powder electrostectrectoric spray gun is connected to the high-voltage electrostectrectectectrtor, when the spray gun electrode is connected to high-voltage electrostrelectrelectrulation, and the work piece positive electrode between the high-voltage electrostation field, and at the muzzle to form a corona discharge. When the powder coating is transported from the powder feeder to the spray gun by purified air and sprayed by the spray gun, the atomized powder captures negative charge in the corona discharge area as a charged particle and flies along the direction of the electric field force to the work surface under the action of airflow and electric field, according to the work piece The distribution density of the surface power line is arranged, which is tightly adsorbed to the surface of the work piece by the effect of the static gravity of The coating film reaches a certain thickness and becomes a uniform flat and smooth coating
2.
after it reaches a certain thickness and is melted by heating and flattening.
2Application of powder coating on thin sheet parts
Anti-corrosion coating of engineering machinery sheet parts includes pre-treatment and coating, generally using phosphate electrophoresis process, and then powder coating or solvent-based coating. The cab and hood are typical sheet parts of construction machinery, the thickness of the plate of such components itself is generally less than
5mm
, heating up quickly in the high temperature curing furnace, the plate baking temperature is uniform, conducive to powder coating.
coating process of thin plate parts in engineering machinery is as follows:
upper part →regreasing→ degreasing→ washing→ washing→ table tone →phosphorusing→ washing →washing→ pure water washing→ cathode electrophoresis → ultrafiltration→ → ultrafiltration→ pure water washing→ leaching→ high temperature curing→ strong cold→ check
/
polishing→ adhesive
/
adhesive tape →employment spray→ manual spraying → high temperature curing→ strong cold→ under the part.
features of thin sheet powder coating:(1) "White" quality requirements are high. Construction machinery in the thin plate is mainly cab and covering parts, the appearance of the quality requirements are quite high, but powder coating generally does not use batch putty grinding process, so the "white parts" surface flatness is better, no defects. Such a sheet of powder coating is only suitable for large-scale construction machinery manufacturers of mass production, the production of sheet parts must use mold stamping, and the quality of the selected plate is better.(2) is coated in a combination of machine spray and manual spray. Due to the relative complexity of the structure of some sheet parts, especially the cab, relying entirely on machine spraying to reach certain parts, especially corners, voids and inner surfaces, manual resurfing is required. Manual coating can be placed before the machine is sprayed, or after the machine is coated, each has its advantages and disadvantages. Artificial re-injection in the machine spray, can prevent leakage, but easy to bring human error, hit the sprayed powder coating surface, because the coating has not been cured, difficult to repair, affecting the final appearance. Artificial re-injection can avoid the above human error before the machine is sprayed, but it is also prone to leakage.(3) baking is heated with gas or fuel and does not require infrared preheating. Because of the thin sheet used, the temperature rises quickly and evenly, the curing requirements of powder coating can be met by heating through hot air circulation.(4) some supporting accessories and shields must have high temperature resistance. Powder coatings have a high curing temperature and must use accessories such as sealants that are resistant to high temperatures. Also really need putty to find a flat place, the selected putty must be conductive high temperature special putty.(5) on the powder coating on the color process is more complex, more suitable for a single color sheet coating. At present, the general use of solvent-based coating in a cured powder coating on the color, because of the powder coating and solvent-based coating adhesion is poor, need to go through secondary baking to improve adhesion. For small areas of color can be replaced by film process, but need to investigate the tape on the long-term adhesion of powder coating, if necessary, need to do accelerated aging test.(6) finished product protection. Since powder coatings have not yet had very mature repair materials and repair processes, the storage, assembly, commissioning and storage of sheet parts need to be well protected.(7) sheet is less expensive to apply with powder than solvent-based coating. Although powder coating and baking energy consumption is higher than solvent-based coating, but the powder coating utilization rate is high, saving coating costs. In addition, the powder chamber's delivery and exhaust fan power is smaller than that of the paint room coated with solvent-based coatings, and the cost of using paint mist flocculants and sewage and exhaust gas treatment can be avoided.
Table
1
is a comparative analysis of the cost of coating during operation of a new sheet powder coating line and a previous solvent-based coating line in a new plant. Because powder coatings are more efficient than solvent-based coatings, coatings coated with powders are much less expensive than solvent-based coatings. Thin sheet parts of the same model can save coating costs
209
yuan/
units compared
to solvent-based coatings.
solvent-based coatings are cured at a low temperature of
60-80
degrees C, with a curing time of
30min
, while powder coating requires a high temperature of
180
C, with a curing time of
40min
. Table
2
is a comparison between powder coating and solvent-based coating baking curing costs, the use of powder coating on a certain type of sheet relative to solvent-based coating to increase the cost of baking curing
81
yuan
/
units.
From the cost of coating and baking energy consumption statistics, the production cost of sheet parts using powder coating process is lower than solvent-based coating process, the cost per square meter of coating can be saved
5
yuan.
3Application of powder coating on structural parts
Engineering mechanical structural parts are mainly welded with thick steel plate or cast forgings molding, the size of the structural parts is larger, powder coating pre-treatment methods and sheet parts have a certain difference.
coating process of the structural parts is as follows:
dressing→ shielding→ top →sulding→ cleaning→ degreasing→ washing→ washing→ table tone→ → phosphate → water wash→ hot water washing→ automatic blowing water→ manual blowing → drying→ drying →smeal powder→ high temperature curing→ strong cold→ the next part.
in the coating of construction machinery structures, the powder coating process compared with solvent-based coating process, has the following characteristics:
(1) pre-treatment process is different. Powder coating on the surface of the work piece requirements are high, can not have grease and dust, otherwise it will affect adhesion, so the powder coating pre-treatment after the blast must also be degreased phosphorus treatment, to ensure that the surface of the work piece clean, and solvent-based coating process on grease and dust tolerance is relatively high, after the blast can be directly after manual cleaning primer coating.
(2) powder coating generally uses a single coating, while solvent-based coating coatings use a double coating. At present, polyester powder coating is generally used in powder coating of construction machinery structures, but its corrosion resistance is slightly worse than that of coating system with epoxy primer and polyurethane finish.(3) powder coating efficiency is high. In the use of powder coating, you can adjust the process parameters, a coating can meet the required film thickness requirements, and the use of solvent-based coatings generally need to spray more than two to achieve the specified film thickness.(4) powder coating using electrostitive spraying, due to the structure of the structure is more complex, there are some groove parts, the presence of the Faraday effect affects the powder coating on the powder effect, resulting in some area leakage or thin spray, and solvent-based coating can use pre-painting process to solve the above problems.(5) powder coating needs to take into account the thickness of the plate of the structural parts and the heat absorption of the steel plate
3
. Due to the thick plate of the structural part, the surface temperature of the work piece rises slowly and requires a long heating time. In order to shorten the heating time, the combination of infrared preheating and hot air furnace cycle heating is generally used, and the energy consumption is much greater than that of solvent-based coating baking. In addition, the structural parts are large and complex, easy to cause uneven distribution of the surface temperature of the work piece, it may appear that the temperature of the outer area of the work piece has exceeded the curing temperature requirements, while the internal temperature of the work piece has not yet reached the curing requirements of the powder coating, so the powder coating is only suitable for use in simpler structural parts.(6) strong cold for a long time. Due to the high temperature of powder coating, it takes a long time of strong cold, which is not conducive to the acceleration of production beats and the improvement of production capacity.
Table
3
is a comparative analysis of the cost of coatings in the course of operation of a new powder coating line and a previous solvent-based coating line for a plant structure. Structural parts of the same model can save $232 million in coating costs compared to solvent-based
coatings
coatings.
powder coating uses infrared heating technology to preheat the structural parts during the baking process, and then heats the structure with a gas-hot air circulation furnace. Table
4
is a comparison of the operating costs of powder coating and solvent-based coating heating equipment, with powder coating increasing baking costs by
257,
yuan compared to solvent-based coating., the general shape of simple, smaller structural parts can be used powder coating process, conducive to environmental protection. On the other hand, in terms of coating cost and baking energy consumption, powder coating operation cost is similar to or slightly more expensive than using solvent-based coating. Powder coating is not suitable for structurally complex and bulky structural parts, but with the development of cryogenic powder coatings, the application of powder coatings in structural parts may be expanded.
4 Application of powder coatings on small parts
construction machinery, a wide variety of small parts, its coating design is more flexible, according to its size, shape and pre-treatment requirements to determine the powder coating process. Some small pieces with thick plate, using blasting, phosphate surface treatment and then spraying powder coating, and for small pipes, fenders and other small parts can not be blasted, can be used degreasing, phosphate surface treatment and then spraying powder coating. Small pieces with high anti-corrosion properties can be coated with phosphated electrophoresis and then sprayed with powder coating.
in small parts, the powder coating process compared with solvent-based coating process, has the following characteristics: (1) Powder coating costs are greatly reduced. Construction machinery small parts are coated with solvent-based coating, due to the small size of the work parts, coating utilization rate is very low, such as pipe and bracket utilization rate of only
20-30%
, while the use of powder coating, powder coating recycling, utilization rate of up to
95%
or more , can greatly reduce the cost of coating. < b